The present invention relates to a method for identifying discs used in an optical disc device for recording/reproducing information on a variety of optical discs, each of which has a recording density different from one another, by irradiating laser beams of different wavelengths.
There has been existing an optical disc device whereby information is reproduced from such optical discs as CD, CD-R, CD-RW and the like by using a long wavelength (780 nm) laser beam and also information is allowed to be reproduced from optical discs such as DVD-5 and DVD-9, each of which has a recording density higher than the ones of the foregoing optical discs, by using a short wavelength (650 nm) laser beam.
However, there is a danger that the recording film of an organic pigment base as used with such optical discs as CD-R and the like may be destroyed when a laser beam with a short wavelength of 650 nm is employed. for reproduction of information from the optical discs. It is necessary to take a sufficient countermeasure to prevent the destruction of the recording film from occurring in order to cope with the foregoing problem and a highly accurate method for identifying discs is needed to deal with the above issue.
With an optical disc unit comprising: a first light source radiating a light beam with a first wavelength for reproducing information from a first optical disc; a second light source radiating a light beam with a wavelength shorter than the first wavelength for reproducing information from a second optical disc having a higher recording density than the recording density of the first optical disc; a convergent device operable to have the light beam of the first wavelength and the light beam of the second wavelength converge on the optical disc, respectively; and a light receiving device operable to receive reflective light from the first optical disc and reflective light from the second optical disc, the present invention provides a method for identifying discs comprising: irradiating the light beam of the first wavelength on the optical disc while the rotation of the optical disc being suspended; recognizing the existence of the first optical disc according to a signal received from the light receiving device when the focus lens of the convergent device is moved in the light irradiating axis direction to the optical disc; irradiating the light beam of the second wavelength on the optical disc while the rotation of the optical disc still being suspended when no existence of the first optical disc is recognized; and recognizing the existence of the second optical disc according to a signal received from the light receiving device when the focusing lens of the convergent device is moved in the light irradiating axis direction to the optical disc.
Thus, the destruction of the previously recorded information caused by irradiating a short wavelength (650 nm) laser beam on a CD-R disc that belongs to the first optical disc can be prevented from taking place.
Further, applying some modification to the foregoing method, when no existence of the first optical disc is recognized upon irradiating the light beam of the first wavelength, a signal received from the light receiving device is memorized and, in succession, the light beam of the second wavelength is irradiated, thereby having the existence of the second disc recognized by a signal received from the light receiving device and then having the foregoing signal memorized. By comparing the values of these two memorized signals, a reconfirmation of countermeasures against a malfunction becomes possible.
The foregoing method allows the CD-R disc belonging to the first optical disc to be identified again even when wrong identification has been made upon irradiating the light beam of the first wavelength, thereby achieving a further enhancement in reliability.